Problem tub drain removal

I am rebuilding our guest bath.Wife wants tub changed out before I build new shower.Heres the problem ,when I went to unscrew drain from drain pipe,all four of the little cross bars sheared off,it has been in 19yrs.I had no trouble changing my wifes drain(brass) in the upstairs tub.Does anyone have any idea how I can get it out without destroying tub?perhaps heat it is a steel tub,I had a 4 way tool I made to unscrew the drains it has nothing to bite on.Any suggestions Please???THanks in advance guys!!>Marvin

Dang that was quick!Thank you so very much between this forum and the tile your world forums ,I have been able to completely redo our 1989 home a room at a time ,saving over 85 to 100,000.00 dollars in labor.My thanks once again for your help>Marvin